It is known that concrete surfaces and the like can be sealed in a waterproof manner by forming or applying thereon a membrane of a bituminous composition, such as asphalt, tar or pitch, which is substantially impermeable to moisture and water vapor. Preformed sheet-like materials useful for this purpose are well known. Examples of these materials are disclosed in U.S. Pat. Nos. 3,741,856, 3,853,682 and 3,900,102. These waterproofing materials have a laminate structure of a support sheet adjacent to a membrane of bituminous composition which has adhesive properties which renders it adherent to the support material and to the substructure, such as a concrete slab, to which it is applied. Laminate structures presently commercially available are supplied in the form of rolls which further comprise a flexible release sheet adjacent to the exposed surface of the bituminous membrane. This release sheet is a required component in the present mode of manufacture and serves, in the end product, to prevent the adhesive membrane from adhering to the sheet immediately adjacent thereto when in roll form. The release sheet does not form a part of the finally applied sheet-like structure which renders a substructure waterproof and, therefore, creates problems of removal and disposal at the job site.
Preformed flexible, sheet-like waterproofing material require the utilization of a release sheet, such as in the form of a siliconized paper, as an integral component in the presently known methods of formation. A release sheet capable of withstanding high temperatures is used as a forming surface upon which a hot semi-fluid bituminous composition, generally having a temperature of about 250.degree. F., or greater, is applied. The composition must be cooled prior to superimposing a polymeric support on its free surface in order to minimize deterioration of the support. The resultant laminate structure, including the release sheet, is then formed into rolls for shipment. Alternately, when support sheets having a non-adherent free surface are used, the formed support/membrane laminate is formed into rolls for storage and shipment by removing the laminate from the release sheet at the end of the manufacturing process.
Recently, waterproofing laminates have been developed which eliminate the need for a separate release sheet. U.S. Pat. No. 4,215,160 to Rosenberg and Gaidis describes a waterproofing laminate comprising a bituminous asphalt layer and a carrier sheet which eliminates the need for a release sheet by applying a release agent, specifically a poly(dimethylsiloxane) base release coating, to the backside of the carrier sheet prior to producing the product roll of laminate. Thus, a release agent-carrier-bituminous asphalt "jelly roll" is formed.
When laminates are applied, adjacent layers are typically overlapped. Unfortunately, when the laminate of the '160 patent is utilized the uppermost laminate's bituminous adhesive layer must be laid down over the release agent coated carrier layer of the already adhered sheet, onto which it cannot stick. Thus, the release agent at the overlapping seam must be scrubbed off with a suitable organic solvent. This practice is undesirable from health, safety and environmental viewpoints. As a result, this type of "paperless" waterproofing laminate has not met with success in the marketplace.